In a nuclear plant, a high pressure steam flows inside an equipment such as a heat exchanger and a pipe. In such a plant, for dealing with something wrong with the equipment, such as a leak of a steam, there is equipped a monitoring apparatus which detects abnormal sound generated by the equipment, then monitors whether there is something wrong with the equipment based on the detected value of the sound.
In a prior art, a standard pattern vector having, as an element, a feature value, such as a power spectrum of a normal sound, is previously registered, then an Euclid distance or an angle between the standard pattern vector and an input pattern vector is calculated. The input pattern vector is produced as a vector having, as an element, a feature value of a sound to be monitored. Further, in a prior art, something wrong in a machine is judged by comparing an allowed value with a calculated value of the Euclid distance or the angle.
Namely, in an N-dimensional space wherein N is equal to a number of kinds of the feature, a similarity of two pattern vectors is numerically evaluated, and then something wrong in the machine is judged based on the evaluated value. The similarity represents the angle or the Euclid distance which is a linear distance between a point of the standard pattern vector and a point of the input pattern vector.
For example, as shown in FIG. 17, a seven-dimensional standard pattern vector 10A is previously registered corresponding to a normal sound 10 of which a shape of a power spectrum is flat. The vector 10A has, an element or component, the power spectrum of the normal sound 10.
Then, corresponding to sounds 11, 12, 13 respectively to be monitored, seven-dimensional input pattern vectors 11A, 12A, 13A are produced. Each energy of monitored sounds 11, 12, 13 is equal to the energy of the normal sound 10, but a shape of a power spectrum of each monitored sounds 11, 12, 13 is different from the normal sound 10. The vector 11A has, an element or component, the power spectrum of the monitored sound 11. The vector 12A has, an element or component, the power spectrum of the monitored sound 12. The vector 13A has, an element or component, the power spectrum of the monitored sound 13. As a measure of a similarity between the standard pattern vector 10A and each of the input pattern vectors 11A, 12A, 13A, the Euclid distance or a cosine of the angle indicated by d11, d12, d13 is calculated.
It is assumed there is a relation between a parameter a and each of monitored sounds 11, 12, 13 as shown in FIG. 17.
Namely, as the relationship shown in FIG. 17, the parameter .alpha. prescribes a change of the each power spectrum shape of sounds 11, 12, 13 from the power spectrum shape of the normal sound 10.
The Euclid distance is obtained as a square root of a value which is a sum of a square of each difference between an element of the standard pattern vector and corresponding element of the input pattern vector. A cosine of the angle is obtained by dividing an inner product of two pattern vectors by a magnitude of two pattern vectors.
By the way, in case of using the Euclid distance or the angle as the measure of the similarity to the normal sound, it happens that the same value is obtained in plural sounds, while a shape of a power spectrum is different from each other. In such a case, it is impossible to distinguish sounds having different feature from each other, thus it is impossible to precisely detect an abnormal sound.
The following is a detailed description.
FIG. 18 shows a change of calculated value d11, d12, d13 of the Euclid distance when the parameter a in FIG. 17 is increased from 0 to 1.
FIG. 19 shows a change of calculated value d11, d12, d13 of the cosine of the angle when the parameter a in FIG. 17 is increased from 0 to 1.
As shown in FIGS. 18 and 19, the calculated value d11, d12, d13 of the Euclid distance or the cosine of the angle are always equal each other (d11=d12=d13). According to an increase of the parameter a, the Euclid distance value d11, d12, d13 are increased and the cosine value d11, d12, d13 of the angle are decreased. The angle itself is increased. By the way, generally a power spectrum shape of a white noise is flat and a power spectrum shape of a normal sound generated by the equipment in normal motion is almost the same as a white noise. A power spectrum shape of a noise is slightly changed according to time. Hereinafter, such slight change is called a "sway."
In FIG. 17, in a case that the parameter a is small, it is assumed that the sounds 11, 12 are "sway" sounds which slightly swayed from the normal sound 10 and that the sounds 13 is an abnormal sound based on a small leak of a steam etc.
As shown in FIGS. 18 and 19, when the parameter a is the same, the Euclid distance or the angle from the normal sound 10 is the same in each monitored sounds 11, 12, 13. Therefore, by comparing the value with an arbitrary determined allowed value, it is judged that all of three sounds 11, 12, 13 are normal, or conversely, it is judged that all of three sounds 11, 12, 13 are abnormal, then it is impossible to distinguish three sounds 11, 12, 13.
On the other hand, it may be considered to register many standard pattern vectors which correspond to the "sway" sounds from the normal sound 10. However, since there is a limitation in available number of registration of the standard pattern vector because of a memory capacity or processing speed of a computer, it is practically limited to distinguish the "sway" sounds generated by the equipment in normal motion from the abnormal generated by a small steam leak.
As mentioned-above, because prior art uses, as a measure of the similarity, the Euclid distance or the angle among two vectors, it is impossible to exactly detect the abnormal sound and it is impossible to judge something wrong in the machine with a greatly sufficient accuracy.
Therefore, an object of the present invention is to provide an apparatus and a method for detecting an abnormal sound, each of which can exactly obtain a geometric distance between the standard pattern vector and the input pattern vector from two vectors.
Another object of the present invention is to provide a method for exactly judging something wrong in a machine by using a value detected by the above-mentioned abnormal sound detection apparatus or method.
Another object of the present invention is to provide a method for detecting a similarity between a standard oscillation such wave as a voice and an arbitrary oscillation wave as a voice to be monitored, which can exactly obtain a geometric distance between the standard pattern vector and the input pattern vector from two vectors.
Another object of the present invention is to provide a method for recognizing a speech by using a similarity of the oscillation wave detected by the above-mentioned similarity detection method.